Preheat oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
In a large bowl, whisk together the gluten-free flour, cocoa powder, baking soda, baking powder, and salt.
In a separate bowl, whisk together the granulated sugar, brown sugar, oil, eggs, and vanilla extract.
Gradually add the wet ingredients to the dry ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined.
Stir in the hot coffee until the batter is smooth.
Pour the batter into the prepared cake pan and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool in the pan for 10 minutes before inverting it onto a wire rack to cool completely.
Frost with your favorite chocolate frosting and enjoy!
Notes
For a richer flavor, use dark chocolate cocoa powder. You can also add chocolate chips to the batter.